The present invention relates to the selective chlorination of ketones and aromatic alcohols and particularly to chlorination with sulfuryl chloride wherein it is desired to maximize products having one chlorine added per carbonyl or aromatic hydroxy.
Chlorinations of organic compounds having functional groups such as ketones, aldehydes and aromatic hydroxies are known generally to produce mixtures of products with different depths of chlorination, i.e. mixtures of monochloro, dichloro and polychloro products.
Sulfuryl chloride is a well-known chlorinating agent for such reactions. While certain substituted molecules preferrentially give monochlorinations, unsubstituted ketones and aromatic hydroxies generally give a mixture of products. This is particularly true of compounds wherein both carbons adjacent the aromatic hydroxy or carbonyl are unsubstituted in the sense of having a hydrogen covalently bonded to each carbon in aromatic molecules and at least two hydrogens covalently bonded to each carbon in nonaromatic compounds such as ketones.
Examples of compounds which react with sulfuryl chloride to form monochlorinated products preferrentially are those wherein one of the two adjacent carbons is substituted: in the case of aromatics such that no hydrogen is present to chlorinate on an ortho carbon, and in the case of ketones such that one of the adjacent carbons is covalently bonded to two other carbons besides the carbonyl and only to one hydrogen, thus being a tertiary carbon whose hydrogen is preferrentially replaced by chlorine. An example of such substituted phenyls is ortho-cresol which is selectively monochlorinated by sulfuryl chloride. An example of a substituted ketone is methyl, i-propyl ketone which is selectively chlorinated to methyl, 1-methyl,1-chloro ethyl ketone.
Certain sulfur-containing compounds are known to affect the chlorination of certain organic compounds and especially phenyls, by sulfuryl chloride. Thus, in work by Bilik et al. in Zhurnal Org Khim. volume 5, number 2, pp. 348-51 (Feb. 19, 1969) and British Pat. No. 1,047,058 certain sulfhydryl compounds are said to moderate the reaction of phenyls with sulfuryl chloride so as to increase the selectivity to monochlorination. Other sulfur compounds are indicated as increasing the reaction rate and the selectivity towards parachlorination in U.S. Pat. No. 3,920,757, while such compounds are said to act as catalysts in Belgium Pat. No. 827,912 abstracted in chemical abstracts 85:123581C.